Intro to Agents of Disease Flashcards
What is Disease?
CHange in state of health of host - resulting in inability to carry out normal function due to the actions of an agent
What is clinical disease?
Obvious change with readily detectable signs of disfunction or illness
What is subclinical disease?
no readily detectible signs of dysfunction or illness –> subtle changes in productivity, growth and fitness
What factors affects HPEI?
agent of disease (pathogen)
Effect on host (pathology)
ost repomse (immunity/inflam and repair)
Enviro (external world reltes to host and pathogen
What is parasitism
Symbiotic relationship between organism and host causes harm to host (disease)
Mutualism
symbiotic relationship that benefits both organism and host
Commensalism
Symbiotic relationship where organism does no obvious harm to host
opportunistic pathogens
organisms that become pathogenic after alternation to hosts health
What % of human infectious diseases have an animal origin?
75%
What causes infectious diseases
The action of infectious agents in the host
What factors influence disease?
Parasitic (pathogen)
host
Environment
What are parasitic factors?
strains
virulence
properties (e.g adaptability)
toxins
dose
method and duration of exposure
What are host factors?
animal species
genotype
age
nutritional status
repro status
past exposure/immunity
concurrent disease/ injuries
immune competence
behaviours
What are environmental factors?
Climate
Altitude/topography
other species
population density
food, water, soil and air
season
What is DNA-DNA Hybridisation?
2 complimentary ss DNA/RNA molecules bind together to form a double stranded molecule
Complementary base pairing
How do we do Viral nomenclature
grouped into families
subdivision by host species affected and clinical disease
What is a strain?
an organism within a species which is a clonal descendent from a single isolate
Gram positive cell wall
long chain polymers
bound to cell membrane and or peptidoglycan
antigenic specificy
Gram neg cell wall
lipopolyssacharide
protect cell against enzymatic attack
endotoxins
aids survival in small intestine
o antigen used in serotype identification
What are the nutrient requirements of bacteria?
water
carbon and energy source
nitrogen and sulphur
phosphorus
other elements
What is the difference between aerobic and anaerobic metabolism?
Aerobic metabolism = respiration
Anaerobic metabolism = fermentation
What is a virion?
The complete infectious virus particle
helical or cubical/icosahedral
Enveloped virus properties:
host phospholipids
glycoproteins of viral origin
lipid rich
sensitive to lipid solvents
more fragile
Non enveloped virus properties:
More resilient
capsid cell surface proteins
- similar functions to the glycoproteins
DNA virus properties:
Double stranded
replicate in nucleus (except poxvirus)
stable and less prone to mutation
persistent infection
temporal regulation of gene transcription
RNA virus properties:
single stranded
linear (can be segmented)
pos or neg sense
pos sense go straight into protein synth
most replicate in cytoplasm
labile (easily changed) and prone to mutation
antigenic drift
Athropod examples
Insects (flies, mozzies, lice)
Acarines (ticks and mites)
Helminths examples:
Nematodes (roundworms)
Cestodes (tapeworms)
Trematodes (flukes)
Arthropod properties:
Ectoparasites
- live on host surface
- vectors
Life cycle
- pupation
- larva and pupa (complete)
- nymph (incomplete)
Nematodes properties:
endoparasites
cylindrical multi-cellular eukaryotes
mouth pieces
repro structures & external features
Direct & indirect life cycles:
Direct = single host animal species
Indirect = no difinitive host (intermediate host)
Cestodes properties:
endoparasitic segmented flatworms
3 parts: neck, strobila, scolex
nutrition absorbed through cuticle
disease associated with attachment and occupation
Trematode properties:
endoparasitic non segmented flatworms
FLUKES
in direct life cycle
Lymnaeid snail
Young migrate through liver
adult develop in bile duct
Protozoa properties
single cell eukaryotes
enveloped
tropism (blood cells)
various modes of motility
inter or intracellular in host
repro asexually and sexually
What is pathogenicity
the quality or state of being pathogenic, the potential ability to produce disease
What is virulence?
The ability of a microorganism to cause damage to its host.
What 3 characteristics of a pathogen determine virulence?
Invasiveness (ability to spread to adjacent tissues)
Infectivity (ability to establish infection)
Pathogenicity (ability of pathogen to cause disease
What are the 3 categories of factors influencing pattern of disease?
Environment (Saprophytes)
Other animals (obligate parasites)
The animal itself (opportunistic pathogens)
What are the 2 forms of transmission?
Vertical (parent to offspring)
Horizontal (between individuals by a physical means)
Modes of horizontal transmission
Direct (suseptible animal in physical contact with infected animal or their infectious secretions)
Indirect (no direct physical contact/ carried from source to suseptible animal/ living (vectors) or non-living (fomites))
Types of vectors
Mechanical (salmonella from animal faeces)
Biological (arboviruses) - mozzies, flies and ticks
Fomites
inanimate objects that transmit agent
e.g. furniture, posts, blankets, milking machienes
